This invention relates to high powered coherent radiation sources and more particularly to a continuously tunable free electron laser which can generate high power in the centimeter, millimeter, and submillimeter range.
During the past ten years, relativistic electron beams have been used with the view of generating intense coherent electromagnetic radiation having wavelengths in the centimeter, millimeter, and submillimeter ranges. Two main types of electron beam instabilities have been used for this purpose: the cyclotron maser instability characterized by azimuthal and axial electron bunching, and emission frequencies associated with the electron gyrofrequency or one of its harmonics, and the free electron laser instability characterized by axial electron bunching, and emission frequencies associated with the Doppler upshifted period of an imposed, transverse, periodic (wiggler) magnetic field.
Each mechanism has its advantages and disadvantages. The cyclotron maser (gyrotron) has a large instability growth rate and good efficiency. However, it is limited in frequency to the millimeter wavelength range due to technical difficulties of constructing practical tubes with very large magnetic fields. The free electron laser has smaller growth rates and efficiencies and has rigid requirements on beam quality. However, because of the double Doppler upshift experienced by the waves, very high frequencies can be achieved with the free electron laser.